DESCRIPTION: The long-term objective of this research is the development of a compact, robust, and user-friendly laser source for 2-photon- excited laser scanning microscopy. Femtosecond-duration pulses from a modelocked solid- state laser operating at wavelengths around 1.3 microns will be frequency- doubled to generate wavelength-tunable pulses in the wavelength range around 650 nanometers. The modelocked laser will be pumped by an array of laser diodes to reduce the size and cost of the source while improving its stability and reliability. Such a source will provide researchers in the biological and biophysical sciences much greater access to nonlinear laser microscopies while enhancing and expanding its capabilities. The source will be designed for compatibility with the large and growing base of laser scanning microscopes. The development of new and/or enhanced capabilities for microscopy will have a significant bearing on health. Improved means for visualizing submicron chemistry will aid the understanding of molecular processes in both normal and diseased states. Intracellular micropharmacology is one directly health-related example of nonlinear laser microscopy: Highly localized and specific treatments become possible by 2-photon uncaging of bioeffector molecules microscopy.